Field of the Invention: The present invention relates to methods of fabricating row lines over a planarized semiconductive grid of a field emission array. Particularly, the present invention relates to row line fabrication methods that employ only two masks to define row lines and pixel openings therethrough.
Background of the Related Art: Typically, field emission displays (xe2x80x9cFEDsxe2x80x9d) include an array of pixels, each of which includes one or more substantially conical emitter tips. The array of pixels of a field emission display is typically referred to as a field emission array. Each of the emitter tips is electrically connected to a negative voltage source by means of a cathode conductor line, which is also typically referred to as a column line.
Another set of electrically conductive lines, which are typically referred to as row lines or as gate lines, extends over the pixels of the field emission array. Row lines typically extend across a field emission display substantially perpendicularly to the direction in which the column lines extend. Accordingly, the paths of a row line and of a column line typically cross proximate (above and below, respectively) the location of an emitter tip. The row lines of a field emission array are electrically connected to a relatively positive voltage source. Thus, as a voltage is applied across the column line and the row line, electrons are emitted by the emitter tips and accelerated through an opening in the row line.
As electrons are emitted by emitter tips and accelerate past the row line that extends over the pixel, the electrons are directed toward a corresponding pixel of a positively charged electro-luminescent panel of the field emission display, which is spaced apart from and substantially parallel to the field emission array. As electrons impact a pixel of the electro-luminescent panel, the pixel is illuminated. The degree to which the pixel is illuminated depends upon the number of electrons that impact the pixel.
An exemplary method of fabricating field emission arrays is taught in U.S. Pat. No. 5,372,973 (hereinafter xe2x80x9cthe ""973 Patentxe2x80x9d), to issued Trung T. Doan et al. on Dec. 13, 1994. The field emission array fabrication method of the ""973 Patent includes an electrically conductive grid, or gate, disposed over the surface thereof and including apertures substantially above each of the emitter tips of the field emission array. Known processes, including chemical mechanical planarization (xe2x80x9cCMPxe2x80x9d) and a subsequent mask and etch, are employed to provide a substantially planar grid surface and to define the apertures therethrough. While the electrically conductive grid of the field emission array disclosed in the ""973 Patent is fabricated from an electrically conductive material such as chromium, field emission displays that include grids of semiconductive material, such as silicon, are also known.
Typically, in fabricating row lines over planarized field emission arrays that include grids of semiconductive material, three separate mask steps and subsequent etches are employed. With reference to FIGS. 1A and 2A, a first mask 28 is typically required to remove semiconductive material of grid 122 from the areas between adjacent rows of emitters tips 114 and thereby define row lines 132 of the remaining portions of the semiconductive grid 122 and expose regions of dielectric layer 120 between adjacent row lines 132. FIGS. 1B and 2B illustrate the use of a second mask 136 to remove conductive material 126, which is deposited over grid 122 of semiconductive material, from the areas between adjacent row lines 132 in order to further define row lines 132 through the conductive material 126, and from the portion of row lines 132 overlying each pixel 112 or emitter tip 114 in order to form pixel openings 140 that facilitate the travel of electrons emitted from emitter tips 114 through apertures 124 of grid 122 and past row lines 132. With reference to FIGS. 1C and 2C, a third mask 150 is required to remove passivation material 134 disposed over row lines 132 from pixel openings 140.
The use of three separate masks undesirably increases fabrication time and costs, as three separate photoresist deposition steps, three separate photoresist exposure steps, and three separate mask removal steps are required. Accordingly, row line fabrication processes that require three mask steps are somewhat inefficient.
Accordingly, there is a need for a field emission array row line fabrication method that requires fewer than three masks and, consequently, that increases the efficiency with which row lines are fabricated while reducing the likelihood of failure of the field emission arrays and the costs associated with fabricating field emission arrays.
The present invention includes a method of fabricating row lines on the planarized semiconductive grid of a field emission display. The row line fabrication method of the present invention employs two masks to define the row lines over the field emission array and pixel openings through the row lines.
According to the present invention, the column lines, emitter tips, overlying semiconductive grid, and apertures through the semiconductor grid above the emitter tips of a field emission array may be fabricated by known processes. The semiconductive grid of the field emission array may be planarized by known processes, such as by known chemical-mechanical planarization (xe2x80x9cCMPxe2x80x9d) techniques. Each pixel of the field emission array may include one or more emitter tips, as known in the art.
A layer of conductive material may then be deposited over the substantially planar surface of the semiconductive grid of the field emission array. A first mask, including apertures alignable between adjacent rows of pixels of the field emission array, is employed to define row lines over the field emission array. The first mask, which may be fabricated by known processes, is disposed over the layer of conductive material. The conductive material that underlies the apertures of the first mask, that is located substantially within a periphery of each of the apertures, and that is exposed through the apertures of the first mask is then removed by known techniques, such as etching. Next, portions of the semiconductive grid that underlie the apertures of the first mask and are located substantially within a periphery of each of the apertures, and that are exposed, are removed, such as by known etching techniques. These portions of the semiconductive grid may be exposed either through the apertures of the first mask or through apertures that were defined through the previously etched layer of conductive material during the removal of conductive material therefrom. As portions of the semiconductive grid of the field emission array are removed, the row lines of the field emission array are defined and the underlying layer of passivation material beneath the semiconductive grid is exposed between adjacent row lines.
A layer of passivation material is then disposed over the surface of the field emission array, including over the row lines of the field emission array. As the conductive material of the row lines and the overlying layer of passivation material are disposed over the semiconductive grid and the field emitters of the field emission array, electrons are prevented from escaping the field emission array. Accordingly, a second mask is employed to define pixel openings through the conductive material of the row lines and through the overlying layer of passivation material.
The second mask, which includes apertures that are alignable over each of the pixels of the field emission array, may be fabricated and disposed over the field emission array as known in the art. After the second mask has been disposed over the field emission array, the passivation material underlying each of the apertures, located substantially within a periphery of each of the apertures, and exposed through the apertures may be removed by known processes, such as etching, to expose the underlying conductive material of the row lines. The conductive material that underlies each of the apertures of the second mask and that is located substantially within a periphery of each of the apertures is then exposed through the second mask or through the passivation layer and may be removed by known processes, such as etching, to expose the underlying semiconductive grid, including the apertures therethrough that are positioned substantially above pixels of the field emission array.
The field emission array may then be assembled with other components of a field emission display, such as the display screen, housing, and other components thereof, as known in the art.
Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings, and the appended claims.